Data communication apparatus and method, data communication system, information-processing apparatus and method, recording medium, and program

ABSTRACT

In an AV-data transfer system, AV data stored in a RAID embedded in an AV server is supplied to a client personal computer connected to a network such as the Internet or an intranet by way of the network, and AV data output by the client personal computer is transmitted to the AV server through the network to be stored in the RAID. The AV server makes accesses to the RAID to write and read out data into and from the RAID. In addition to the AV server, the AV-data transfer system also includes another personal computer for exchanging AV data with the client personal computer and receiving a variety of commands from the client personal computer by way of the network in accordance with an FTP (File Transfer Protocol). As a result, it is possible to fast handle access requests made by a larger number of client personal computers.

BACKGROUND OF THE INVENTION

[0001] In general, the present invention relates to a data communicationapparatus, a data communication method, a data communication system, aninformation-processing apparatus, an information-processing method,recording mediums and programs. More particularly, the present inventionrelates to a data communication apparatus, a data communication method,a data communication system, an information-processing apparatus and aninformation-processing method, which are appropriate for use incommunication of data through an information recording medium having alarge storage capacity and through a network, relates to programs forimplementing the data communication method and theinformation-processing method and relates to recording mediums forstoring the programs.

[0002] When AV data is communicated among client personal computers 4through a large-capacity information recording medium such as RAID(Redundant Array of Independent Disks) 1 and through a network 3 such asthe Internet and an intranet as shown in FIG. 1, there is conceived theuse of a system employing a server personal computer 2 for controllingaccesses to the RAID 1 and processing requests for an access to the RAID1, which are made by the client personal computers 4.

[0003] The RAID 1 for storing AV data is connected to the network 3through the personal computer (PC) 2. Connected to the network 3, apersonal computer 4 is capable of making a request for an access to theRAID 1.

[0004] The personal computer 2 processes accesses to the RAID 1 andtransfers of data through the network 3. To put it concretely, when thepersonal computer 4 makes a request for a transfer of AV data stored inthe RAID 1 by way of the network 3, the personal computer 2 accepts therequest, subsequently makes an access to the RAID 1 to acquire therequested AV data and temporarily stores the data in a memory embeddedin the personal computer 2 before transferring the data to the personalcomputer 4 by way of the network 3.

[0005] As described above, the personal computer 2 processes accesses tothe RAID 1 and transfers of data through the network 3. Thus, whenrequests for such an access are made by a plurality of personalcomputers 4 through the network 3 at the same time, it is necessary forthe personal computer 2 to process the accesses to the RAID 1 and aplurality of data transfers by way of the network 3 concurrently.However, the personal computer 2 is not capable of processing both theaccesses and the data transfers at the same time. As a result, there isa limit on the number of accesses that can be handled and there is thusraised a problem of a reduced processing speed.

SUMMARY OF THE INVENTION

[0006] It is thus an object of the present invention addressing theproblem described above to implement a data communication system capableof handling a larger number of accesses to a RAID quickly by employing aplurality of apparatuses for independently processing such accesses andtransfers of data by way of a network.

[0007] A data communication apparatus provided by the present inventionis characterized in that the data communication apparatus comprises:

[0008] an acceptance means for accepting a request for a communicationthrough a network from a terminal connected to the network;

[0009] a communication means for communicating data with the connectedterminal by way of the network;

[0010] an issuance means for issuing an access command and a controlcommand to a data storage unit in accordance with a request for acommunication received by the acceptance means;

[0011] a holding means for holding an access command issued by theissuance means, data received from the terminal and data to betransmitted to the terminal;

[0012] a first control means for controlling the acceptance means, thecommunication means, the issuance means and the holding means;

[0013] a control-command-buffering means for buffering a control commandissued by the issuance means;

[0014] a fetching means for fetching a control command buffered in thecontrol-command-buffering means;

[0015] an acquisition means for acquiring an access command held by theholding means in accordance with a control command fetched by thefetching means;

[0016] an output means for outputting an access command acquired by theacquisition means to the data storage unit;

[0017] a data-buffering means for buffering data to be stored in thedata storage unit or data read out from the data storage unit;

[0018] a transfer means for transferring data between the holding meansand the data-buffering means in accordance with a control commandfetched by the fetching means; and

[0019] a second control means for controlling thecontrol-command-buffering means, the fetching means, the acquisitionmeans, the output means, the data-buffering means and transfer means,

[0020] wherein the first and second control means operate independentlyof each other.

[0021] A RAID can be used as the data storage unit.

[0022] A data communication method provided by the present invention ischaracterized in that the data communication method comprises:

[0023] an acceptance step of accepting a request for a communicationthrough a network from a terminal connected to the network;

[0024] a communication step of communicating data with the connectedterminal by way of the network;

[0025] an issuance step of issuing an access command and a controlcommand to a data storage unit in accordance with a request for acommunication received in processing carried out at the acceptance step;

[0026] a holding step of holding an access command issued in processingcarried out at the issuance step, data received from the terminal anddata to be transmitted to the terminal;

[0027] a first control step of controlling pieces of processing carriedout at the acceptance step, the communication step, the issuance stepand the holding step;

[0028] a control-command-buffering step of buffering a control commandissued in the processing carried out at the issuance step;

[0029] a fetching step of fetching a control command buffered inprocessing carried out at the control-command-buffering step;

[0030] an acquisition step of acquiring an access command held in theprocessing carried out at the holding step in accordance with a controlcommand fetched in processing carried out at the fetching step;

[0031] an output step of outputting an access command acquired inprocessing carried out at the acquisition step to the data storage unit;

[0032] a data-buffering step of buffering data to be stored in the datastorage unit or data read out from the data storage unit;

[0033] a transfer step of transferring data between the processingcarried out at the holding step and processing carried out at thedata-buffering step in accordance with a control command fetched in theprocessing carried out at the fetching step; and

[0034] a second control step of controlling pieces of processing carriedout at the control-command-buffering step, the fetching step, theacquisition step, the output step, the data-buffering step and transferstep,

[0035] wherein pieces of processing at the first and second controlsteps are carried out independently of each other.

[0036] A first recording medium provided by the present invention ischaracterized in that the first recording medium is used for storing aprogram comprising:

[0037] an acceptance step of accepting a request for a communicationthrough a network from a terminal connected to the network;

[0038] a communication step of communicating data with the connectedterminal by way of the network;

[0039] an issuance step of issuing an access command and a controlcommand to a data storage unit in accordance with a request for acommunication received in processing carried out at the acceptance step;

[0040] a holding step of holding an access command issued in processingcarried out at the issuance step, data received from the terminal anddata to be transmitted to the terminal;

[0041] a first control step of controlling pieces of processing carriedout at the acceptance step, the communication step, the issuance stepand the holding step;

[0042] a control-command-buffering step of buffering a control commandissued in the processing carried out at the issuance step;

[0043] a fetching step of fetching a control command buffered inprocessing carried out at the control-command-buffering step;

[0044] an acquisition step of acquiring an access command held in theprocessing carried out at the holding step in accordance with a controlcommand fetched in processing carried out at the fetching step;

[0045] an output step of outputting an access command acquired inprocessing carried out at the acquisition step to the data storage unit;

[0046] a data-buffering step of buffering data to be stored in the datastorage unit or data read out from the data storage unit;

[0047] a transfer step of transferring data between the processingcarried out at the holding step and processing carried out at thedata-buffering step in accordance with a control command fetched in theprocessing carried out at the fetching step; and

[0048] a second control step of controlling pieces of processing carriedout at the control-command-buffering step, the fetching step, theacquisition step, the output step, the data-buffering step and transferstep,

[0049] wherein pieces of processing at the first and second controlsteps are carried out independently of each other.

[0050] A first program provided by the present invention ischaracterized in that the first program comprises:

[0051] an acceptance step of accepting a request for a communicationthrough a network from a terminal connected to the network;

[0052] a communication step of communicating data with the connectedterminal by way of the network;

[0053] an issuance step of issuing an access command and a controlcommand to a data storage unit in accordance with a request for acommunication received in processing carried out at the acceptance step;

[0054] a holding step of holding an access command issued in processingcarried out at the issuance step, data received from the terminal anddata to be transmitted to the terminal;

[0055] a first control step of controlling pieces of processing carriedout at the acceptance step, the communication step, the issuance stepand the holding step;

[0056] a control-command-buffering step of buffering a control commandissued in the processing carried out at the issuance step;

[0057] a fetching step of fetching a control command buffered inprocessing carried out at the control-command-buffering step;

[0058] an acquisition step of acquiring an access command held in theprocessing carried out at the holding step in accordance with a controlcommand fetched in processing carried out at the fetching step;

[0059] an output step of outputting an access command acquired inprocessing carried out at the acquisition step to the data storage unit;

[0060] a data-buffering step of buffering data to be stored in the datastorage unit or data read out from the data storage unit;

[0061] a transfer step of transferring data between the processingcarried out at the holding step and processing carried out at thedata-buffering step in accordance with a control command fetched in theprocessing carried out at the fetching step; and

[0062] a second control step of controlling pieces of processing carriedout at the control-command-buffering step, the fetching step, theacquisition step, the output step, the data-buffering step and transferstep,

[0063] wherein pieces of processing at the first and second controlsteps are carried out independently of each other.

[0064] A data communication system provided by the present invention ischaracterized in that the data communication system comprises a firstinformation-processing apparatus for communicating data with a terminalconnected to a network by way of the network and a secondinformation-processing apparatus for controlling accesses to a datastorage unit wherein:

[0065] the first information-processing apparatus comprises:

[0066] an acceptance means for accepting a request for a communicationthrough the network from the terminal connected to the network;

[0067] a communication means for communicating data with the connectedterminal by way of the network;

[0068] an issuance means for issuing an access command and a controlcommand to the data storage unit in accordance with a request for acommunication received by the acceptance means;

[0069] a holding means for holding an access command issued by theissuance means, data received from the terminal and data to betransmitted to the terminal; and

[0070] a supplying means for supplying a control command issued by theissuance means to the second information-processing apparatus; whereas

[0071] the second information-processing apparatus comprises:

[0072] a control-command-buffering means for buffering a control commandreceived from the supplying means;

[0073] a fetching means for fetching a control command buffered in thecontrol-command-buffering means;

[0074] an acquisition means for acquiring an access command held by theholding means in accordance with a control command fetched by thefetching means;

[0075] an output means for outputting an access command acquired by theacquisition means to the data storage unit;

[0076] a data-buffering means for buffering data to be stored in thedata storage unit or data read out from the data storage unit; and

[0077] a transfer means for transferring data between the holding meansand the data-buffering means in accordance with a control commandfetched by the fetching means.

[0078] A RAID can be used as the data storage unit.

[0079] A first information-processing apparatus provided by the presentinvention is characterized in that the first information-processingapparatus comprises:

[0080] an acceptance means for accepting a request for a communicationthrough a network from a terminal connected to the network;

[0081] a communication means for communicating data with the connectedterminal by way of the network;

[0082] an issuance means for issuing an access command and a controlcommand to a data storage unit in accordance with a request for acommunication received by the acceptance means;

[0083] a holding means for holding an access command issued by theissuance means, data received from the terminal and data to betransmitted to the terminal; and

[0084] a supplying means for supplying a control command issued by theissuance means to another information-processing apparatus forcontrolling the data storage unit.

[0085] A RAID can be used as the data storage unit.

[0086] A first information-processing method provided by the presentinvention is characterized in that the first information-processingmethod comprises:

[0087] an acceptance step of accepting a request for a communicationthrough a network from a terminal connected to the network;

[0088] a communication step of communicating data with the connectedterminal by way of the network;

[0089] an issuance step of issuing an access command and a controlcommand to a data storage unit in accordance with a request for acommunication received in processing carried out at the acceptance step;

[0090] a holding step of holding an access command issued in processingcarried out at the issuance step, data received from the terminal anddata to be transmitted to the terminal; and

[0091] a supplying step of supplying a control command issued in theprocessing carried out at the issuance step to anotherinformation-processing apparatus for controlling the data storage unit.

[0092] A second recording medium provided by the present invention ischaracterized in that the second recording medium is used for storing aprogram comprising:

[0093] an acceptance step of accepting a request for a communicationthrough a network from a terminal connected to the network;

[0094] a communication step of communicating data with the connectedterminal by way of the network;

[0095] an issuance step of issuing an access command and a controlcommand to a data storage unit in accordance with a request for acommunication received in processing carried out at the acceptance step;

[0096] a holding step of holding an access command issued in processingcarried out at the issuance step, data received from the terminal anddata to be transmitted to the terminal; and

[0097] a supplying step of supplying a control command issued in theprocessing carried out at the issuance step to anotherinformation-processing apparatus for controlling the data storage unit.

[0098] A second program provided by the present invention ischaracterized in that the second program comprises:

[0099] an acceptance step of accepting a request for a communicationthrough a network from a terminal connected to the network;

[0100] a communication step of communicating data with the connectedterminal by way of the network;

[0101] an issuance step of issuing an access command and a controlcommand to a data storage unit in accordance with a request for acommunication received in processing carried out at the acceptance step;

[0102] a holding step of holding an access command issued in processingcarried out at the issuance step, data received from the terminal anddata to be transmitted to the terminal; and

[0103] a supplying step of supplying a control command issued in theprocessing carried out at the issuance step to anotherinformation-processing apparatus for controlling the data storage unit.

[0104] A second information-processing apparatus provided by the presentinvention is characterized in that the second information-processingapparatus comprises:

[0105] a control-command-buffering means for buffering a control commandreceived from another information-processing apparatus;

[0106] a fetching means for fetching a control command buffered in thecontrol-command-buffering means;

[0107] an acquisition means for acquiring an access command held by theother information-processing apparatus from the otherinformation-processing apparatus in accordance with a control commandfetched by the fetching means;

[0108] an output means for outputting an access command acquired by theacquisition means to a data storage unit;

[0109] a data-buffering means for buffering data to be stored in thedata storage unit or data read out from the data storage unit; and

[0110] a transfer means for transferring data between the otherinformation-processing apparatus and the data-buffering means inaccordance with a control command fetched by the fetching means.

[0111] A RAID can be used as the data storage unit.

[0112] A second information-processing method provided by the presentinvention is characterized in that the second information-processingmethod comprises:

[0113] a control-command-buffering step of buffering a control commandreceived from another information-processing apparatus;

[0114] a fetching step of fetching a control command buffered inprocessing carried out at the control-command-buffering step;

[0115] an acquisition step of acquiring an access command held by theother information-processing apparatus from the otherinformation-processing apparatus in accordance with a control commandfetched in processing carried out at the fetching step;

[0116] an output step of outputting an access command acquired inprocessing carried out at the acquisition step to a data storage unit;

[0117] a data-buffering step of buffering data to be stored in the datastorage unit or data read out from the data storage unit; and

[0118] a transfer step of transferring data between the otherinformation-processing apparatus and processing carried out at thedata-buffering step in accordance with a control command fetched in theprocessing carried out at the fetching step.

[0119] A third recording medium provided by the present invention ischaracterized in that the third recording medium is used for storing aprogram comprising:

[0120] a control-command-buffering step of buffering a control commandreceived from another information-processing apparatus;

[0121] a fetching step of fetching a control command buffered inprocessing carried out at the control-command-buffering step;

[0122] an acquisition step of acquiring an access command held by theother information-processing apparatus from the otherinformation-processing apparatus in accordance with a control commandfetched in processing carried out at the fetching step;

[0123] an output step of outputting an access command acquired inprocessing carried out at the acquisition step to a data storage unit;

[0124] a data-buffering step of buffering data to be stored in the datastorage unit or data read out from the data storage unit; and

[0125] a transfer step of transferring data between the otherinformation-processing apparatus and processing carried out at thedata-buffering step in accordance with a control command fetched in theprocessing carried out at the fetching step.

[0126] A third program provided by the present invention ischaracterized in that the third program comprises:

[0127] a control-command-buffering step of buffering a control commandreceived from another information-processing apparatus;

[0128] a fetching step of fetching a control command buffered inprocessing carried out at the control-command-buffering step;

[0129] an acquisition step of acquiring an access command held by theother information-processing apparatus from the otherinformation-processing apparatus in accordance with a control commandfetched in processing carried out at the fetching step;

[0130] an output step of outputting an access command acquired inprocessing carried out at the acquisition step to a data storage unit;

[0131] a data-buffering step of buffering data to be stored in the datastorage unit or data read out from the data storage unit; and

[0132] a transfer step of transferring data between the otherinformation-processing apparatus and processing carried out at thedata-buffering step in accordance with a control command fetched in theprocessing carried out at the fetching step.

[0133] In the data communication apparatus, the data communicationmethod and the first program, which are provided by the presentinvention,

[0134] a request for a communication is accepted through a network froma terminal connected to the network;

[0135] data is communicated with the connected terminal by way of thenetwork;

[0136] an access command and a control command are issued to a datastorage unit in accordance with a received request for a communication;

[0137] an issued access command, data received from the terminal anddata to be transmitted to the terminal are held in a holding means;

[0138] the processing of accepting a request for a communication, theprocessing of communicating data, the processing of issuing an accesscommand and a control command to the data storage unit as well as theprocessing of holding an issued access command, data received from theterminal and data to be transmitted to the terminal are controlled by afirst control means;

[0139] an issued control command is stored in a command buffer;

[0140] a control command is fetched from the command buffer;

[0141] an access command is acquired from the holding means inaccordance with a control command fetched from the command buffer;

[0142] an acquired access command is output to the data storage unit;

[0143] data to be stored in the data storage unit or data read out fromthe data storage unit is stored in a data buffer;

[0144] data is transferred between the holding means and the data bufferin accordance with a control command fetched from the command buffer;and

[0145] the processing of storing of a control command in the commandbuffer, the processing of fetching a control command from the commandbuffer, the processing of acquiring an access command from the holdingmeans, the processing of outputting an access command to the datastorage unit, the processing of storing data in the data buffer and theprocessing of transferring data between the holding means and the databuffer are controlled by a second control means.

[0146] It should be noted that the first and second control means areexecuted independently of each other.

[0147] As a result, it is possible to fast handle access requests madeby a larger number of terminals.

[0148] In the first information-processing apparatus employed in thedata communication system provided by the present invention,

[0149] a request for a communication is accepted through a network froma terminal connected to the network;

[0150] data is communicated with the connected terminal by way of thenetwork;

[0151] an access command and a control command are issued to a datastorage unit in accordance with a received request for a communication;

[0152] an issued access command, data received from the terminal anddata to be transmitted to the terminal are held in a holding means; and

[0153] an issued control command is supplied to the secondinformation-processing apparatus.

[0154] On the other hand, in the second information-processing apparatusemployed in the data communication system,

[0155] an issued control command is stored in a command buffer;

[0156] a control command is fetched from the command buffer;

[0157] an access command is acquired from the holding means inaccordance with a control command fetched from the command buffer;

[0158] an acquired access command is output to the data storage unit;

[0159] data to be stored in the data storage unit or data read out fromthe data storage unit is stored in a data buffer; and

[0160] data is transferred between the holding means and the data bufferin accordance with a control command fetched from the command buffer.

[0161] As a result, it is possible to fast handle access requests madeby a larger number of terminals.

[0162] In the first information-processing apparatus, the firstinformation-processing method and the second program, which are providedby the present invention,

[0163] a request for a communication is accepted through a network froma terminal connected to the network;

[0164] data is communicated with the connected terminal by way of thenetwork;

[0165] an access command and a control command are issued to a datastorage unit in accordance with a received request for a communication;

[0166] an issued access command, data received from the terminal anddata to be transmitted to the terminal are held in a holding means; and

[0167] an issued control command is supplied to anotherinformation-processing apparatus for controlling the data storage unit.

[0168] As a result, it is possible to fast handle access requests madeby a larger number of terminals.

[0169] In the second information-processing apparatus, the secondinformation-processing method and the third program, which are providedby the present invention,

[0170] a control command received from another information-processingapparatus is stored in a command buffer;

[0171] a control command is fetched from the command buffer;

[0172] an access command held by the other information-processingapparatus is acquired from the other information-processing apparatus inaccordance with a control command fetched from the command buffer;

[0173] an acquired access command is output to the data storage unit;

[0174] data to be stored in the data storage unit or data read out fromthe data storage unit is stored in a data buffer; and

[0175] data is transferred between the other information-processingapparatus and the data buffer in accordance with a control commandfetched from the command buffer.

[0176] As a result, it is possible to fast handle access requests madeby a larger number of terminals.

[0177] The above and other objects, features and advantages of thepresent invention will become apparent from the following descriptionand the appended claims, taken in conjunction with the accompanyingdrawings in which like parts or elements denoted by like referencesymbols.

BRIEF DESCRIPTION OF THE DRAWINGS

[0178]FIG. 1 is a block diagram showing a typical conventional systemfor transferring data through a network;

[0179]FIG. 2 is a block diagram showing a typical configuration of anAV-data transfer system implemented by an embodiment of the presentinvention;

[0180]FIG. 3 is a block diagram showing a typical configuration of apersonal computer on the AV server side in FIG. 2;

[0181]FIG. 4 is a block diagram showing a typical configuration of theAV server in FIG. 2;

[0182]FIG. 5 is a flowchart representing file transfer processingcarried out by the personal computer on the AV server side in FIG. 2;

[0183]FIG. 6 is a flowchart representing a write processing carried outby a CPU shown in FIG. 3;

[0184]FIG. 7 is a flowchart representing a read processing carried outby the CPU;

[0185]FIG. 8 is a flowchart representing file transfer processingcarried out by the AV server;

[0186]FIG. 9 is a flowchart representing DMA-Command-Down processing;

[0187]FIG. 10 is a flowchart representing DMA-Data-Down processing;

[0188]FIG. 11 is a flowchart representing DMA-Data-Up processing;

[0189]FIG. 12 is a flowchart representing RAID-Command-Down processing;

[0190]FIG. 13 is a flowchart representing RAID-Data-Down processing; and

[0191]FIG. 14 is a flowchart representing RAID-Data-Up processing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0192] An AV-data transfer system provided by the present invention isexplained by referring to FIG. 2. The AV-data transfer system suppliesAV data stored in a RAID 43 shown in FIG. 4 to a personal computer 4connected to a network 3 such as the Internet or an intranet by way ofthe network 3. On the other hand, the AV-data transfer system alsoreceives AV data output from the personal computer 4 and stores the datainto the RAID 43 through the network 3.

[0193] The AV-data transfer system comprises a personal computer 11 andan AV server 12. The personal computer 11 exchanges AV data with thepersonal computer 4 and receives a variety of commands from the personalcomputer 4 through the network 3 in accordance with an FTP (FileTransfer Protocol). As shown in FIG. 4, the AV server 12 has the RAID 43incorporated therein. The AV server 12 makes accesses to the RAID 43 toread out and write data from and into the RAID 43.

[0194]FIG. 3 is a diagram showing a typical configuration of thepersonal computer 11. The personal computer 11 includes a CPU (CentralProcessing Unit) 21 for controlling file transfer processing byexecution of a predetermined program. The file transfer processing willbe described later in detail. The CPU 21 is connected to a bus 24. Thebus 24 is connected to a ROM (Read-Only Memory) 22 and a RAM (RandomAccess Memory) 23. The ROM 22 is used for storing programs including aBIOS (Basic Input Output System), which is executed at an activationtime. On the other hand, the RAM 23 is used for temporarily storing aprogram and various kinds of data.

[0195] In addition, the bus 24 is also connected to a storage unit 25, anetwork interface (I/F) 26 and an AV-server interface (I/F) 27. Thestorage unit 25 typically includes a hard-disk drive for storingprograms and AV data. The network interface 26 is used for communicatingAV data with the personal computer 4 and receiving a variety of commandsfrom the personal computer 4 through the network 3 in accordance with aTCP/IP (Transmission Control Protocol/Internet Protocol). Connected tothe AV server 12, the AV-server interface 27 communicates a variety ofcommands and AV data with the AV server 12.

[0196] As described above, the CPU 21 employed in the personal computer11 carries out file transfer processing by execution of a programinstalled in the hard-disk drive included in the storage unit 25. Theprogram is loaded from the storage unit 25 into the RAM 23 in accordancewith a command issued by the CPU 21 at the end of activation of thepersonal computer 11.

[0197]FIG. 4 is a diagram showing a typical configuration of the AVserver 12. The AV server 12 includes a CPU 31 for controlling processingto be described later by execution of a program stored in a ROM 32 inaccordance with a control command stored in a control-command buffer 38.The CPU 31 is connected to a bus 34. The bus 34 is connected to a ROM 32and a RAM 33. The ROM 32 is used for storing programs to be executed bythe CPU 31. The RAM 33 serves as a work area of program execution and isused for storing a file system. The file system is information showing arelation between file names and addresses of sectors in the RAID 43,which are used for storing data of the files indicated by the filenames.

[0198] The bus 34 is also connected to a DMA (Direct Memory Access)controller 35 controlled by the CPU 31, an execution flag register 36,an end flag register 37, the control-command buffer 38, a RAID-commandbuffer 40 and a frame buffer 41.

[0199] The DMA controller 35 controls DMA transfers of control commandsthrough an interface (I/F) 39 between the personal computer 11 and thecontrol-command buffer 38, DMA transfers of RAID commands through theinterface 39 between the personal computer 11 and the RAID-commandbuffer 40 and DMA transfers of data through the interface 39 between thepersonal computer 11 and the frame buffer 41. A DMA transfer is atransfer of a command or data by adoption of the so-called DMAtechnique.

[0200] The execution flag register 36 is a flag for storing informationindicating completion of an processing carried out by the personalcomputer 11 to write control commands into the control-command buffer 38through the interface 39.

[0201] The end flag register 37 is a flag for storing informationindicating completion of all processing carried out by the CPU 31 inaccordance with control commands stored in the control-command buffer38.

[0202] The control-command buffer 38 is used for storing controlcommands, which were each transferred by the personal computer 11 to thecontrol-command buffer 38 by way of the interface 39 by adopting the DMAtechnique.

[0203] To be more specific, the control-command buffer 38 is used forstoring 6 different control commands, namely, DMA-Command-Down,DMA-Data-Down, DMA-Data-Up, RAID-Command-Down, RAID-Data-Down andRAID-Data-Up, which are explained as follows.

[0204] DMA-Command-Down is a control command for driving the DMAcontroller 35 employed in the AV server 12 to carry out a DMA transferof a RAID command from the RAM 23 employed in the personal computer 11to the RAID-command buffer 40 employed in the AV server 12.

[0205] DMA-Data-Down is a control command for driving the DMA controller35 employed in the AV server 12 to carry out a DMA transfer of AV datafrom the RAM 23 employed in the personal computer 11 to the frame buffer41 employed in the AV server 12.

[0206] DMA-Data-Up is a control command for driving the DMA controller35 employed in the AV server 12 to carry out a DMA transfer of AV datafrom the frame buffer 41 employed in the AV server 12 to the RAM 23employed in the personal computer 11.

[0207] RAID-Command-Down is a control command for requesting the CPU 31employed in the AV server 12 to output a RAID command stored in theRAID-command buffer 40 to the RAID 43 by way of a multiplexer 42.

[0208] RAID-Data-Down is a control command for requesting the CPU 31employed in the AV server 12 to output AV data stored in the framebuffer 41 to the RAID 43 by way of the multiplexer 42.

[0209] RAID-Data-Up is a control command for requesting the CPU 31employed in the AV server 12 to read out AV data from the RAID 43 andstore the data in the frame buffer 41.

[0210] Refer back to FIG. 4. The interface 39 is connected to thepersonal computer 11.

[0211] The RAID-command buffer 40 is used for temporarily storing RAIDcommands each used for controlling the RAID 43. A RAID command stored inthe RAID-command buffer 40 was transferred from the personal computer 11by way of the interface 39 by adoption of the DMA technique.

[0212] The following description explains 2 RAID commands, namely, readand write commands. A write command is a command for storing AV datasupplied to the AV server 12 into the RAID 43 as a file indicated by aspecified file name. A read command is a command for reading out AV dataof a file indicated by a specified file name from the RAID 43.

[0213] Refer back to FIG. 4. The frame buffer 41 is used for temporarilyholding AV data transferred from the personal computer 11 by way of theinterface 39 by adoption of the DMA technique before storing the AV datainto the RAID 43. On the other hand, the frame buffer 41 is also usedfor temporarily holding AV data read out from the RAID 43 before beingtransferred to the personal computer 11 by way of the interface 39 byadoption of the DMA technique.

[0214] The multiplexer (MUX) 42 selects a RAID command held in theRAID-command buffer 40 or AV data held in the frame buffer 41 and storesthe selected one into the RAID 43.

[0215] The RAID 43 outputs AV data read out by a read command receivedfrom the multiplexer 42 as a RAID command from a sector addressassociated with a specified file name to the frame buffer 41 in a readprocessing according to the command. On the other hand, the RAID 43 alsostores AV data from the RAID 43 at a sector address associated with aspecified file name in accordance with a write command received from themultiplexer 42 as a RAID command in a write processing requested by thecommand.

[0216] Next, the processing of the AV-data transfer system is explainedby referring to flowcharts shown in FIGS. 5 to 14.

[0217] First of all, file transfer processing carried out by thepersonal computer 11 is described by referring to the flowchart shown inFIG. 5. The file transfer processing is started by the CPU 21 byexecution of a program stored in the ROM 22 after the personal computer11 is activated.

[0218] At a step S1, the CPU 21 forms a judgment as to whether or notthe personal computer 4 has made an access to the personal computer 11through the network 3. The judgment is formed repeatedly till theoutcome of the judgment indicates that the personal computer 4 has madean access. As the personal computer 4 makes an access, the flow of theprocessing goes on to a step S2.

[0219] At a step S2, the CPU 21 forms a judgment as to whether or notthe access made by the personal computer 4 is a PUT command, which is acommand requesting the AV data output by the personal computer 4 bestored in the AV server 12. If the outcome of the judgment indicatesthat the access made by the personal computer 4 is a PUT command, theflow of the processing goes on to a step S3. At the step S3, the CPU 21controls the network interface 26 to receive AV data transmitted by thepersonal computer 4 through the network 3 and stores the data in the RAM23.

[0220] Then, at the next step S4, the CPU 21 carries out a writeprocessing to store the AV data in the AV server 12. Details of thewrite processing are explained by referring to the flowchart shown inFIG. 6. At a step S11, the CPU 21 generates a write command, which isone of RAID commands, and stores the write command in the RAM 23 alongwith a file name specified by the personal computer 4 as the name of afile into which the AV data is to be stored. Then, at the next step S12,the CPU 21 transfers a DMA-Command-Down control command to thecontrol-command buffer 38 employed in the AV server 12 by way of theAV-server interface 27.

[0221] Subsequently, at the next step S13, the CPU 21 transfers aDMA-Data-Down control command to the control-command buffer 38 employedin the AV server 12 by way of the AV-server interface 27. Then, at thenext step S14, the CPU 21 transfers a RAID-Command-Down control commandto the control-command buffer 38 employed in the AV server 12 by way ofthe AV-server interface 27. Subsequently, at the next step S15, the CPU21 transfers a RAID-Data-Down control command to the control-commandbuffer 38 employed in the AV server 12 by way of the AV-server interface27.

[0222] Then, at the next step S16, the CPU 21 sets the execution flagregister 36 employed in the AV server 12 through the AV-server interface27 at 1 to indicate that a sequence of control commands have been storedin the control-command buffer 38. On the other hand, the CPU 21 resetsthe end flag register 37 employed in the AV server 12 at 0 to indicatethat processing requested by the control commands has not beencompleted.

[0223] Subsequently, at the next step S17, the CPU 21 examines the endflag register 37 employed in the AV server 12 through the AV-serverinterface 27 to form a judgment as to whether or not the end flagregister 37 has been set at 1 to indicate that the sequence of controlcommands stored in the control-command buffer 38 have all been executed.The judgment is formed repeatedly till the outcome of the judgmentindicates that the end flag register 37 has been set at 1. As theoutcome of the judgment indicates that the end flag register 37 has beenset at 1, the write processing is finished and the flow of theprocessing goes back to the step S1 of the flowchart shown in FIG. 5 torepeat the processing of this step and the subsequent steps.

[0224] If the outcome of the judgment formed at the step S2 of theflowchart shown in FIG. 5 indicates that the access made by the personalcomputer 4 is not a PUT command, on the other hand, the flow of theprocessing goes on to a step S5. At the step S5, the CPU 21 forms ajudgment as to whether or not the access made by the personal computer 4is a GET command, which is a command requesting the AV server 12 to readout AV data stored in the RAID 43 and transmit the data to the personalcomputer 11. If the outcome of the judgment indicates that the accessmade by the personal computer 4 is a GET command, the flow of theprocessing goes on to a step S6.

[0225] At the step S6, the CPU 21 carries out a read processing to readout the AV data from the AV server 12. Details of the read processingare explained by referring to the flowchart shown in FIG. 7. At a stepS21, the CPU 21 generates a read command, which is one of RAID commands,and stores the read command in the RAM 23 along with a file namespecified by the personal computer 4 as the name of a file from whichthe AV data is to be read out. Then, at the next step S22, the CPU 21transfers a DMA-Command-Down control command to the control-commandbuffer 38 employed in the AV server 12 by way of the AV-server interface27.

[0226] Subsequently, at the next step S23, the CPU 21 transfers aRAID-Command-Down control command to the control-command buffer 38employed in the AV server 12 by way of the AV-server interface 27. Then,at the next step S24, the CPU 21 transfers a RAID-Data-Up controlcommand to the control-command buffer 38 employed in the AV server 12 byway of the AV-server interface 27. Subsequently, at the next step S25,the CPU 21 transfers a DMA-Data-Up control command to thecontrol-command buffer 38 employed in the AV server 12 by way of theAV-server interface 27.

[0227] Then, at the next step S26, the CPU 21 sets the execution flagregister 36 employed in the AV server 12 through the AV-server interface27 at 1 to indicate that a sequence of control commands have been storedin the control-command buffer 38. On the other hand, the CPU 21 resetsthe end flag register 37 employed in the AV server 12 at 0 to indicatethat processing requested by the control commands has not beencompleted.

[0228] Subsequently, at the next step S27, the CPU 21 examines the endflag register 37 employed in the AV server 12 through the AV-serverinterface 27 to form a judgment as to whether or not the end flagregister 37 has been set at 1 to indicate that the sequence of controlcommands stored in the control-command buffer 38 have all been executed.The judgment is formed repeatedly till the outcome of the judgmentindicates that the end flag register 37 has been set at 1. As theoutcome of the judgment indicates that the end flag register 37 has beenset at 1, the read processing is finished and the flow of the processinggoes back to a step S7 of the flowchart shown in FIG. 5.

[0229] As a result of processing carried out by the AV server 12 toaccompany the read processing described above, the AV data read out fromthe RAID 43 is stored in the RAM 23 employed in the personal computer11. The processing carried out by the AV server 12 to accompany the readprocessing described above will be described later. At the step S7, theCPU 21 controls the network interface 26 to transmit the AV data storedin the RAM 23 to the personal computer 4 by way of the network 3. Then,the flow of the processing goes back to the step S1 to repeat theprocessing at this step and the subsequent steps.

[0230] If the outcome of the judgment formed at the step S5 indicatesthat the access made by the personal computer 4 is not a GET command, onthe other hand, the flow of the processing goes back to the step S1 torepeat the processing at this step and the subsequent steps.

[0231] As described above, the personal computer 11 mainly exchanges AVdata with the personal computer 4 through the network 3, generates aRAID command to be output to the CPU 31 employed in the AV server 12 andtransfers a control command to the control-command buffer 38 employed inthe AV server 12.

[0232] By referring to a flowchart shown in FIG. 8, the followingdescription explains processing carried out by the AV server 12 toaccompany the file transfer processing, that is, the write and readprocessings, carried out by the personal computer 11 as described above.The processing carried out by the AV server 12 is started by executionof a program stored in the ROM 32 by the CPU 31 after the AV server 12is activated.

[0233] At a step S31, the CPU 31 forms a judgment as to whether or notthe execution flag register 36 is set at 1. The judgment is formedrepeatedly till the outcome of the judgment indicates that the executionflag register 36 is set at 1. As the outcome of the judgment indicatesthat the execution flag register 36 is set at 1, the flow of theprocessing goes on to a step S32.

[0234] At the step S32, the CPU 31 fetches a control command from thecontrol-command buffer 38 and deletes the command from thecontrol-command buffer 38.

[0235] Then, at the next step S33, the CPU 31 forms a judgment as towhether or not the control command fetched at the step S32 isDMA-Command-Down. If the outcome of the judgment indicates that thecontrol command fetched at the step S32 is DMA-Command-Down, the flow ofthe processing goes on to a step S34 to carry out DMA-Command-Downprocessing represented by a flowchart shown in FIG. 9. Then, the flow ofthe processing goes on to a step S45. It should be noted that, if theoutcome of the judgment indicates that the control command fetched atthe step S32 is not DMA-Command-Down, on the other hand, the flow of theprocessing goes on to a step S35.

[0236] At the step S35, the CPU 31 forms a judgment as to whether or notthe control command fetched at the step S32 is DMA-Data-Down. If theoutcome of the judgment indicates that the control command fetched atthe step S32 is DMA-Data-Down, the flow of the processing goes on to astep S36 to carry out DMA-Data-Down processing represented by aflowchart shown in FIG. 10. Then, the flow of the processing goes on tothe step S45. It should be noted that, if the outcome of the judgmentindicates that the control command fetched at the step S32 is notDMA-Data-Down, on the other hand, the flow of the processing goes on toa step S37.

[0237] At the step S37, the CPU 31 forms a judgment as to whether or notthe control command fetched at the step S32 is DMA-Data-Up. If theoutcome of the judgment indicates that the control command fetched atthe step S32 is DMA-Data-Up, the flow of the processing goes on to astep S38 to carry out DMA-Data-Up processing represented by a flowchartshown in FIG. 11. Then, the flow of the processing goes on to the stepS45. It should be noted that, if the outcome of the judgment indicatesthat the control command fetched at the step S32 is not DMA-Data-Up, onthe other hand, the flow of the processing goes on to a step S39.

[0238] At the step S39, the CPU 31 forms a judgment as to whether or notthe control command fetched at the step S32 is RAID-Command-Down. If theoutcome of the judgment indicates that the control command fetched atthe step S32 is RAID-Command-Down, the flow of the processing goes on toa step S40 to carry out RAID-Command-Down processing represented by aflowchart shown in FIG. 12. Then, the flow of the processing goes on tothe step S45. It should be noted that, if the outcome of the judgmentindicates that the control command fetched at the step S32 is notRAID-Command-Down, on the other hand, the flow of the processing goes onto a step S41.

[0239] At the step S41, the CPU 31 forms a judgment as to whether or notthe control command fetched at the step S32 is RAID-Data-Down. If theoutcome of the judgment indicates that the control command fetched atthe step S32 is RAID-Data-Down, the flow of the processing goes on to astep S42 to carry out RAID-Data-Down processing represented by aflowchart shown in FIG. 13. Then, the flow of the processing goes on tothe step S45. It should be noted that, if the outcome of the judgmentindicates that the control command fetched at the step S32 is notRAID-Data-Down, on the other hand, the flow of the processing goes on toa step S43.

[0240] At the step S43, the CPU 31 forms a judgment as to whether or notthe control command fetched at the step S32 is RAID-Data-Up. If theoutcome of the judgment indicates that the control command fetched atthe step S32 is RAID-Data-Up, the flow of the processing goes on to astep S44 to carry out RAID-Data-Up processing represented by a flowchartshown in FIG. 14. Then, the flow of the processing goes on to the stepS45. It should be noted that, if the outcome of the judgment indicatesthat the control command fetched at the step S32 is not RAID-Data-Up, onthe other hand, the flow of the processing goes on to the step S45.

[0241] At the step S45, the CPU 31 forms a judgment as to whether or notall control commands stored in the control-command buffer 38 have beenfetched. If the outcome of the judgment indicates that control commandsstored in the control-command buffer 38 have not all been fetched, theflow of the processing goes back to the step S32 to repeat theprocessing of this step and the subsequent steps. If the outcome of thejudgment formed at the step S45 indicates that control commands storedin the control-command buffer 38 have all been fetched, on the otherhand, the flow of the processing goes on to a step S46.

[0242] At the step S46, the CPU 31 sets the end flag register 37 at 1and resets the execution flag register 36 to 0.

[0243] Next, by referring to the flowchart shown in FIG. 9, thefollowing description explains the DMA-Command-Down processing carriedout at the step S34. At a step S51, the CPU 31 controls the DMAcontroller 35 to transfer a RAID command and a file name from the RAM 23employed in the personal computer 11 to the AV server 12 by adoption ofthe DMA technique. The RAID command can be a read or write command. TheDMA controller 35 then starts to transfer the RAID command and the filename from the RAM 23 employed in the personal computer 11 to the AVserver 12 in accordance with the control executed by the CPU 31.

[0244] Then, at the next step S52, the CPU 31 forms a judgment as towhether or not the processing carried out by the DMA controller 35 totransfer the RAID command and the file name from the RAM 23 employed inthe personal computer 11 to the AV server 12 has been completed. Thejudgment is formed repeatedly till the outcome of the judgment indicatesthat the processing carried out by the DMA controller 35 to transfer theRAID command and the file name from the RAM 23 employed in the personalcomputer 11 to the AV server 12 has been completed. As the outcome ofthe judgment indicates that the processing carried out by the DMAcontroller 35 to transfer the RAID command and the file name from theRAM 23 employed in the personal computer 11 to the AV server 12 has beencompleted, the flow of the processing goes on to a step S53. At the stepS53, the CPU 31 controls the DMA controller 35 to store the transferredRAID command and the transferred file names in the RAID-command buffer40. Upon completion of the processing of this step, the DMA-Command-Downprocessing is finished.

[0245] Next, by referring to the flowchart shown in FIG. 10, thefollowing description explains the DMA-Data-Down processing carried outat the step S36. At a step S61, the CPU 31 controls the DMA controller35 to transfer AV data from the RAM 23 employed in the personal computer11 to the RAID 43 employed in the AV server 12 by adoption of the DMAtechnique. The DMA controller 35 then starts to transfer the AV datafrom the RAM 23 employed in the personal computer 11 to the AV server 12in accordance with the control executed by the CPU 31.

[0246] Then, at the next step S62, the CPU 31 forms a judgment as towhether or not the processing carried out by the DMA controller 35 totransfer the AV data from the RAM 23 employed in the personal computer11 to the AV server 12 has been completed. The judgment is formedrepeatedly till the outcome of the judgment indicates that theprocessing carried out by the DMA controller 35 to transfer the AV datafrom the RAM 23 employed in the personal computer 11 to the AV server 12has been completed. As the outcome of the judgment indicates that theprocessing carried out by the DMA controller 35 to transfer AV data fromthe RAM 23 employed in the personal computer 11 to the AV server 12 hasbeen completed, the flow of the processing goes on to a step S63. At thestep S63, the CPU 31 controls the DMA controller 35 to store thetransferred AV data in the frame buffer 41. Upon completion of theprocessing of this step, the DMA-Data-Down processing is finished.

[0247] Next, by referring to the flowchart shown in FIG. 11, thefollowing description explains the DMA-Data-Up processing carried out atthe step S38. At a step S71, the CPU 31 controls the DMA controller 35to transfer AV data read out from the RAID 43 and stored in the framebuffer 41 to the RAM 23 employed in the personal computer 11 by adoptionof the DMA technique. The DMA controller 35 then starts to transfer theAV data from the frame buffer 41 to the RAM 23 employed in the personalcomputer 11 by adoption of the DMA technique in accordance with thecontrol executed by the CPU 31. Upon completion of the processing ofthis step, the DMA-Data-Up processing is finished.

[0248] Next, by referring to the flowchart shown in FIG. 12, thefollowing description explains the RAID-Command-Down processing carriedout at the step S40. At a step S81, the CPU 31 fetches a RAID commandand a file name from the RAID-command buffer 40. Then, at the next stepS82, the CPU 31 forms a judgment as to whether the RAID command fetchedat the step S81 is a read or write command. If the outcome of thejudgment indicates that the RAID command fetched at the step S81 is awrite command, the flow of the processing goes on to a step S83.

[0249] At the step S83, the CPU 31 creates a new file indicated by thefile name fetched at the step S81 and allocates the address of a sectorfor storing AV data in the RAID 43. The CPU 31 then catalogs the filename in the file system stored in the RAM 33 by associating the filename with the address of the sector.

[0250] Then, at the next step S84, the CPU 31 stores the sector addressassociated with the file name in the RAID-command buffer 40.Subsequently, at the next step S85, the CPU 31 outputs the RAID commandand the sector address from the RAID-command buffer 40 to the RAID 43.

[0251] If the outcome of the judgment formed at the step S82 indicatesthat the RAID command fetched at the step S81 is a read command, on theother hand, the flow of the processing goes on to a step S86.

[0252] At the step S86, the CPU 31 searches the file system stored inthe RAM 33 for a sector address associated with the file name fetched atthe step S81. The sector address is the address of a sector in the RAID43. In this sector, AV data to be read out is stored. The flow of theprocessing then goes on to the step S84. Upon completion of theprocessing of the step S85, the RAID-Command-Down processing isfinished.

[0253] Next, by referring to the flowchart shown in FIG. 13, thefollowing description explains the RAID-Data-Down processing carried outat the step S42. At a step S91, the CPU 31 controls the multiplexer 42to select AV data stored in the frame buffer 41 and output the data tothe RAID 43 to be stored therein. Upon completion of the processing ofthe step S91, the RAID-Data-Down processing is finished.

[0254] Next, by referring to the flowchart shown in FIG. 14, thefollowing description explains the RAID-Data-Up processing carried outat the step S44. At a step S101, the CPU 31 controls the frame buffer 41to store AV data read out from the RAID 43. Upon completion of theprocessing of the step S101, the RAID-Data-Up processing is finished.

[0255] As described above, the AV server 1 writes and reads out AV datainto and from the RAID 43 on the basis of a control command stored inthe control-command buffer 38 by the personal computer 11.

[0256] Thus, since accesses to the RAID 43 are controlled by the CPU 31of the AV server 12 in the AV-data transfer system while AV data isexchanged with the personal computer 4 through the network 3 inaccordance with control executed by the CPU 21 employed in the personalcomputer 11 in a manner completely independent of the CPU 31, it ispossible to handle a larger number of requests for accesses made at thesame time.

[0257] It should be noted that the present invention can be applied totransfers of not only AV data but also all kinds of data through anetwork.

[0258] In the AV-data transfer system implemented by the embodiment ofthe present invention, the personal computer 11 and the AV server 12 are2 separate apparatuses. However, they can be combined and incorporatedin the same cabinet as an apparatus for implementing the functions ofthe CPU 21, the CPU 31 and the RAID 43.

[0259] It should be noted that, in this specification, steps describinga program stored in a recording medium can of course be pieces ofprocessing, which are carried out in a prescribed order along the timeaxis, but do not have to be executed sequentially. That is to say, thesteps can be pieces of processing, which are carried out concurrently orindividually.

[0260] In addition, the phrase data communication system and the AV-datatransfer system used in this specification each mean the whole systemcomprising a plurality of apparatuses.

[0261] While a preferred embodiment of the present invention has beendescribed using specific terms, such description is for illustrativepurposes only, and it is to be understood that changes and variationsmay be made without departing from the spirit or scope of the followingclaims.

What is claimed is:
 1. A data communication apparatus for controllingcommunications of data between a terminal and a data storage unit by wayof a network, said data communication apparatus comprising: anacceptance means for accepting a request for a communication throughsaid network from said terminal connected to said network; acommunication means for communicating data with said connected terminalby way of said network; an issuance means for issuing an access commandand a control command to said data storage unit in accordance with arequest for a communication received by said acceptance means; a holdingmeans for holding an access command issued by said issuance means, datareceived from said terminal and data to be transmitted to said terminal;a first control means for controlling said acceptance means, saidcommunication means, said issuance means and said holding means; acontrol-command-buffering means for buffering a control command issuedby said issuance means; a fetching means for fetching a control commandbuffered in said control-command-buffering means; an acquisition meansfor acquiring an access command held by said holding means in accordancewith a control command fetched by said fetching means; an output meansfor outputting an access command acquired by said acquisition means tosaid data storage unit; a data-buffering means for buffering data to bestored in said data storage unit or data read out from said data storageunit; a transfer means for transferring data between said holding meansand said data-buffering means in accordance with a control commandfetched by said fetching means; and a second control means forcontrolling said control-command-buffering means, said fetching means,said acquisition means, said output means, said data-buffering means andtransfer means, wherein said first and second control means operateindependently of each other.
 2. A data communication apparatus accordingto claim 1 wherein said data storage unit is a RAID.
 3. A datacommunication method adopted by a data communication apparatus forcontrolling communications of data between a terminal and a data storageunit by way of a network, said data communication method comprising: anacceptance step of accepting a request for a communication through saidnetwork from said terminal connected to said network; a communicationstep of communicating data with said connected terminal by way of saidnetwork; an issuance step of issuing an access command and a controlcommand to said data storage unit in accordance with a request for acommunication received in processing carried out at said acceptancestep; a holding step of holding an access command issued in processingcarried out at said issuance step, data received from said terminal anddata to be transmitted to said terminal; a first control step ofcontrolling pieces of processing carried out at said acceptance step,said communication step, said issuance step and said holding step; acontrol-command-buffering step of buffering a control command issued insaid processing carried out at said issuance step; a fetching step offetching a control command buffered in processing carried out at saidcontrol-command-buffering step; an acquisition step of acquiring anaccess command held in said processing carried out at said holding stepin accordance with a control command fetched in processing carried outat said fetching step; an output step of outputting an access commandacquired in processing carried out at said acquisition step to said datastorage unit; a data-buffering step of buffering data to be stored insaid data storage unit or data read out from said data storage unit; atransfer step of transferring data between said processing carried outat said holding step and processing carried out at said data-bufferingstep in accordance with a control command fetched in said processingcarried out at said fetching step; and a second control step ofcontrolling pieces of processing carried out at saidcontrol-command-buffering step, said fetching step, said acquisitionstep, said output step, said data-buffering step and transfer step,wherein pieces of processing at said first and second control steps arecarried out independently of each other.
 4. A recording medium forstoring a computer readable program for controlling communications ofdata between a terminal and a data storage unit by way of a networkwherein said program comprises: an acceptance step of accepting arequest for a communication through said network from said terminalconnected to said network; a communication step of communicating datawith said connected terminal by way of said network; an issuance step ofissuing an access command and a control command to said data storageunit in accordance with a request for a communication received inprocessing carried out at said acceptance step; a holding step ofholding an access command issued in processing carried out at saidissuance step, data received from said terminal and data to betransmitted to said terminal; a first control step of controlling piecesof processing carried out at said acceptance step, said communicationstep, said issuance step and said holding step; acontrol-command-buffering step of buffering a control command issued insaid processing carried out at said issuance step; a fetching step offetching a control command buffered in processing carried out at saidcontrol-command-buffering step; an acquisition step of acquiring anaccess command held in said processing carried out at said holding stepin accordance with a control command fetched in processing carried outat said fetching step; an output step of outputting an access commandacquired in processing carried out at said acquisition step to said datastorage unit; a data-buffering step of buffering data to be stored insaid data storage unit or data read out from said data storage unit; atransfer step of transferring data between said processing carried outat said holding step and processing carried out at said data-bufferingstep in accordance with a control command fetched in said processingcarried out at said fetching step; and a second control step ofcontrolling pieces of processing carried out at saidcontrol-command-buffering step, said fetching step, said acquisitionstep, said output step, said data-buffering step and transfer step,wherein pieces of processing at said first and second control steps arecarried out independently of each other.
 5. A program to be executed bya computer for controlling communications of data between a terminal anda data storage unit by way of a network, said program comprising: anacceptance step of accepting a request for a communication through saidnetwork from said terminal connected to said network; a communicationstep of communicating data with said connected terminal by way of saidnetwork; an issuance step of issuing an access command and a controlcommand to said data storage unit in accordance with a request for acommunication received in processing carried out at said acceptancestep; a holding step of holding an access command issued in processingcarried out at said issuance step, data received from said terminal anddata to be transmitted to said terminal; a first control step ofcontrolling pieces of processing carried out at said acceptance step,said communication step, said issuance step and said holding step; acontrol-command-buffering step of buffering a control command issued insaid processing carried out at said issuance step; a fetching step offetching a control command buffered in processing carried out at saidcontrol-command-buffering step; an acquisition step of acquiring anaccess command held in said processing carried out at said holding stepin accordance with a control command fetched in processing carried outat said fetching step; an output step of outputting an access commandacquired in processing carried out at said acquisition step to said datastorage unit; a data-buffering step of buffering data to be stored insaid data storage unit or data read out from said data storage unit; atransfer step of transferring data between said processing carried outat said holding step and processing carried out at said data-bufferingstep in accordance with a control command fetched in said processingcarried out at said fetching step; and a second control step ofcontrolling pieces of processing carried out at saidcontrol-command-buffering step, said fetching step, said acquisitionstep, said output step, said data-buffering step and transfer step,wherein pieces of processing at said first and second control steps arecarried out independently of each other.
 6. A data communication systemcomprising a first information-processing apparatus for communicatingdata with a terminal connected to a network by way of said network and asecond information-processing apparatus for controlling accesses to adata storage unit wherein: said first information-processing apparatuscomprises: an acceptance means for accepting a request for acommunication through said network from said terminal connected to saidnetwork; a communication means for communicating data with saidconnected terminal by way of said network; an issuance means for issuingan access command and a control command to said data storage unit inaccordance with a request for a communication received by saidacceptance means; a holding means for holding an access command issuedby said issuance means, data received from said terminal and data to betransmitted to said terminal; and a supplying means for supplying acontrol command issued by said issuance means to said secondinformation-processing apparatus; whereas said secondinformation-processing apparatus comprises: a control-command-bufferingmeans for buffering a control command received from said supplyingmeans; a fetching means for fetching a control command buffered in saidcontrol-command-buffering means; an acquisition means for acquiring anaccess command held by said holding means in accordance with a controlcommand fetched by said fetching means; an output means for outputtingan access command acquired by said acquisition means to said datastorage unit; a data-buffering means for buffering data to be stored insaid data storage unit or data read out from said data storage unit; anda transfer means for transferring data between said holding means andsaid data-buffering means in accordance with a control command fetchedby said fetching means.
 7. A data communication system according toclaim 6 wherein said data storage unit is a RAID.
 8. Aninformation-processing apparatus for communicating data with a terminalconnected to a network by way of said network, saidinformation-processing apparatus comprising: an acceptance means foraccepting a request for a communication through said network from saidterminal connected to said network; a communication means forcommunicating data with said connected terminal by way of said network;an issuance means for issuing an access command and a control command toa data storage unit in accordance with a request for a communicationreceived by said acceptance means; a holding means for holding an accesscommand issued by said issuance means, data received from said terminaland data to be transmitted to said terminal; and a supplying means forsupplying a control command issued by said issuance means to anotherinformation-processing apparatus for controlling said data storage unit.9. An information-processing apparatus according to claim 8 wherein assaid data storage unit is a RAID.
 10. An information-processing methodadopted by an information-processing apparatus for communicating datawith a terminal connected to a network by way of said network, saidinformation-processing method comprising: an acceptance step ofaccepting a request for a communication through said network from saidterminal connected to said network; a communication step ofcommunicating data with said connected terminal by way of said network;an issuance step of issuing an access command and a control command to adata storage unit in accordance with a request for a communicationreceived in processing carried out at said acceptance step; a holdingstep of holding an access command issued in processing carried out atsaid issuance step, data received from said terminal and data to betransmitted to said terminal; and a supplying step of supplying acontrol command issued in said processing carried out at said issuancestep to another information-processing apparatus for controlling saiddata storage unit.
 11. A recording medium for storing a computerreadable program for communicating data with a terminal connected to anetwork by way of said network wherein said program comprises: anacceptance step of accepting a request for a communication through saidnetwork from said terminal connected to said network; a communicationstep of communicating data with said connected terminal by way of saidnetwork; an issuance step of issuing an access command and a controlcommand to a data storage unit in accordance with a request for acommunication received in processing carried out at said acceptancestep; a holding step of holding an access command issued in processingcarried out at said issuance step, data received from said terminal anddata to be transmitted to said terminal; and a supplying step ofsupplying a control command issued in said processing carried out atsaid issuance step to another information-processing apparatus forcontrolling said data storage unit.
 12. A program to be executed by acomputer for communicating data with a terminal connected to a networkby way of said network, said program comprising: an acceptance step ofaccepting a request for a communication through said network from saidterminal connected to said network; a communication step ofcommunicating data with said connected terminal by way of said network;an issuance step of issuing an access command and a control command to adata storage unit in accordance with a request for a communicationreceived in processing carried out at said acceptance step; a holdingstep of holding an access command issued in processing carried out atsaid issuance step, data received from said terminal and data to betransmitted to said terminal; and a supplying step of supplying acontrol command issued in said processing carried out at said issuancestep to another information-processing apparatus for controlling saiddata storage unit.
 13. An information-processing apparatus forcontrolling accesses to a data storage unit, said information-processingapparatus comprising: a control-command-buffering means for buffering acontrol command received from another information-processing apparatus;a fetching means for fetching a control command buffered in saidcontrol-command-buffering means; an acquisition means for acquiring anaccess command held by said other information-processing apparatus fromsaid other information-processing apparatus in accordance with a controlcommand fetched by said fetching means; an output means for outputtingan access command acquired by said acquisition means to said datastorage unit; a data-buffering means for buffering data to be stored insaid data storage unit or data read out from said data storage unit; anda transfer means for transferring data between said otherinformation-processing apparatus and said data-buffering means inaccordance with a control command fetched by said fetching means.
 14. Aninformation-processing apparatus according to claim 13 wherein said datastorage unit is a RAID.
 15. An information-processing method adopted byan information-processing apparatus for controlling accesses to a datastorage unit, said information-processing method comprising: acontrol-command-buffering step of buffering a control command receivedfrom another information-processing apparatus; a fetching step offetching a control command buffered in processing carried out at saidcontrol-command-buffering step; an acquisition step of acquiring anaccess command held by said other information-processing apparatus fromsaid other information-processing apparatus in accordance with a controlcommand fetched in processing carried out at said fetching step; anoutput step of outputting an access command acquired in processingcarried out at said acquisition step to said data storage unit; adata-buffering step of buffering data to be stored in said data storageunit or data read out from said data storage unit; and a transfer stepof transferring data between said other information-processing apparatusand processing carried out at said data-buffering step in accordancewith a control command fetched in said processing carried out at saidfetching step.
 16. A recording medium for storing a computer readableprogram for controlling accesses to a data storage unit wherein saidprogram comprises: a control-command-buffering step of buffering acontrol command received from another information-processing apparatus;a fetching step of fetching a control command buffered in processingcarried out at said control-command-buffering step; an acquisition stepof acquiring an access command held by said other information-processingapparatus from said other information-processing apparatus in accordancewith a control command fetched in processing carried out at saidfetching step; an output step of outputting an access command acquiredin processing carried out at said acquisition step to said data storageunit; a data-buffering step of buffering data to be stored in said datastorage unit or data read out from said data storage unit; and atransfer step of transferring data between said otherinformation-processing apparatus and processing carried out at saiddata-buffering step in accordance with a control command fetched in saidprocessing carried out at said fetching step.
 17. A program to beexecuted by a computer for controlling accesses to a data storage unit,said program comprising: a control-command-buffering step of buffering acontrol command received from another information-processing apparatus;a fetching step of fetching a control command buffered in processingcarried out at said control-command-buffering step; an acquisition stepof acquiring an access command held by said other information-processingapparatus from said other information-processing apparatus in accordancewith a control command fetched in processing carried out at saidfetching step; an output step of outputting an access command acquiredin processing carried out at said acquisition step to said data storageunit; a data-buffering step of buffering data to be stored in said datastorage unit or data read out from said data storage unit; and atransfer step of transferring data between said otherinformation-processing apparatus and processing carried out at saiddata-buffering step in accordance with a control command fetched in saidprocessing carried out at said fetching step.